The North American Numbering Plan (NANP) is an integrated telephone numbering plan for twenty-five regions in twenty countries, primarily in North America and the Caribbean. This group is historically known as World Numbering Zone 1 and has the country code 1. Some North American countries, most notably Mexico, do not participate in the NANP.

The concepts of the NANP were devised originally during the 1940s by the American Telephone and Telegraph Company (AT&T) for the Bell System and the independent telephone companies in North America in Operator Toll Dialing. The first task was to unify the diverse local telephone numbering plans that had been established during the preceding decades, with the goal to speed call completion times and decrease the costs for long-distance calling, by reducing manual labor by switchboard operators. Eventually, it prepared the continent for direct-dialing of long-distance calls by customers, first possible in 1951, which expanded across the nation during the decades following. AT&T continued to administer the continental numbering plan and the technical infrastructure until the end of the Bell System, when operation was delegated to the North American Numbering Plan Administration (NANPA), a service that has been procured from the private sector by the Federal Communications Commission (FCC) in the United States. Each participating country forms a regulatory authority that has plenary control of local numbering resources. The FCC also serves as the U.S. regulator. Canadian numbering decisions are made by the Canadian Numbering Administration Consortium.

The NANP divides the territories of its members into numbering plan areas (NPAs) which are encoded numerically with a three-digit telephone number prefix, commonly termed the area code. Each telephone is assigned a seven-digit telephone number unique only within its respective numbering plan area. The telephone number consists of a three-digit central office (or exchange) code and a four-digit station number. The combination of an area code and the telephone number serves as a destination routing address in the public switched telephone network (PSTN). The North American Numbering Plan conforms with International Telecommunication Union (ITU) Recommendation E.164, which establishes an international numbering framework.

From the Bell System's beginnings in 1876 and throughout the first part of the 20th century, telephone networks grew from essentially local or regional telephone systems. These systems expanded by growing their subscriber bases, as well as enlarging their service areas by implementing additional local exchanges that were interconnected with tie trunks. It was the responsibility of each local administration to devise telephone numbering plans that accommodated the local requirements and growth. As a result, the North American telephone service industry developed into an unorganized set of many differing local numbering systems. The diversity impeded the efficient operation and interconnection of exchanges into a nationwide system for long-distance telephone communication. By the 1940s, the Bell System set out to unify the various existing numbering plans to provide a unified, systematic concept for routing telephone calls across the nation, and to provide efficient long-distance service that eventually did not require the involvement of switchboard operators.

In October 1947, AT&T published the first nationwide numbering plan in coordination with the independent telephone operators. The plan divided most of North America into eighty-six numbering plan areas (NPAs). Each NPA was assigned a unique three-digit code, typically termed NPA code or simply area code. These codes were first used in Operator Toll Dialing by long-distance operators in establishing calls via trunks between toll offices. The goal of automatic service required additional technical advances in the latest generation of toll-switching systems, completed by the early 1950s, and installation of new toll-switching systems in most numbering plan areas. The first customer-dialed direct call using an area code was made on November 10, 1951, from Englewood, New Jersey, to Alameda, California. Direct distance dialing (DDD) was introduced subsequently across the country. By the early 1960s, DDD had become commonplace in cities and most towns in the United States and Canada. By 1967, the number of assigned area codes had grown to 129.

The status of the network of the 1960s was reflected by a new name used in technical documentation: North American Integrated Network. By 1975, the numbering plan was referred to as the North American Numbering Plan, resulting in the well-known initialism NANP, as other countries sought or considered joining the standardization.

Although Bermuda and the Caribbean islands had been assigned the area code 809 as early as 1958 by the administrators at AT&T, individual participating countries or territories had no autonomy over their numbering plan as they received centrally assigned central office prefixes that needed to be unique from those of other countries with the same area code. Regions in Mexico with high call volumes to and from the US were assigned functional area codes as early as 1963, for the purpose of call routing, but a nationwide system of participation in the NANP eventually failed.^{[citation needed]}

During the decades following, the NANP expanded to include all of the United States and its territories, Canada, Bermuda, and seventeen nations of the Caribbean.